European patent 0 112 548 discloses a method for the preparation of active magnesium hydride-magnesium-hydrogen storage systems which absorb hydrogen reversibly. In this method magnesium hydride or metallic magnesium is reacted in finely divided form by contact with a solution of a metal complex and/or an organometallic compound of a metal of the 4th to the 8th subsidiary group of the periodic system, optionally in the presence of hydrogen. The respective transition metal is deposited at the surface of the magnesium hydride and/or the magnesium particles.
As doping agent (precipitant), especially nickel complexes and/or organonickel compounds are used, the bis(cyclooctadiene)-nickel-(O) complex, Ni(COD).sub.2, being particularly preferred. This complex is suspended in toluene or tetrahydrofuran together with the finely divided magnesium. Either the complex is decomposed thermally or the complexly bound cyclooctadiene is hydrogenated to cyclooctane, the nickel being precipitated in each case. The precipitated nickel is deposited on the surface of the magnesium.
However, the doping reagent, Ni(COD).sub.2, is expensive, toxic and difficult to handle. Catalysts, for example, induce a progressive decomposition.